Powder metallurgy articles



1952 c. G. GOETZEL ETAL POWDER METALLURGY ARTICLE Filed Dec. 31,

IN VEN T 0R5 60467366 By 0114 4 El, J I,

Patented Jan. 1, 1 952 2,581,252 POWDER METALLURGY ARTICLES Claus G.Goetzel, Yonkers, and John L. Ellis, New York, N. Y., assignors toSintercast Corporation of America, New York, N. Y., a corporation of NewYork Application December 31, 1947, Serial No. 795,102

Claims. '(CI. 75-22) The invention relates to a turbine blade for use atelevated temperatures, which is composed of substances having difierentmelting points, and particularly to a sintered skeleton of a relativelyskeleton because the particles of the powdered material will not bedistributed evenly within the mold, or distributed in the mold in thedesired pattern. In prior impregnation processes, sizing high meltingpoint formed with interconnecting 5 and machining frequently have beennecessary pores substantially throughout its entirety, the following theimpregnation step. One reason is pores being permeated with aninfiltrant metal, the uneven distribution of the second metal on theexeterior faces of the turbine blade having the surface of the skeleton,which is caused by a coating thereon of the infiltrant metal.uncontrollable adherence of the second metal Heat resistant metallicarticles such as blades, to the surface of the skeleton, andnon-uniformity buckets, valves and the like for jet engines, thereof.rockets, or gas turbines and the like are not satis- One of the objectsof the invention is to profactory when made by conventional casting orvide a shaped article having improved physical forging methods. One ofthe reasons is that characteristics, including high hot tensile thetemperature at which the article is formed is strength, high hot fatiguestrength, high resistnear that of the operating temperature of theeleance to creep at elevated temperatures, and espement in service andit thus is apparent that the cially high corrosion resistance underconditions element would not be strong and stable in its of operation.dimensions under operating conditions. Another The shaped article of thepresent invention difiiculty is that the materials which maintaincomprises a continuous skeleton of high melting their strength atelevated temperatures under point made from powdered materials suitablyprotective atmospheric conditions are subject to sintered, the skeletonstructure having intercomcorrosion under the conditions of operation ofmunicating pores substantially throughout its enelements such as gasturbine blades, and this tirety. The pores of the skeleton are permeatedtends to impair rapidly their strength. throughout by a network of aninfiltrant metallic Powder metallurgy methods must be used in material,and a layer of corrosion resistant meorder to meet the high temperaturerequirements tallic material is formed on the faces of the in articllelsin 1the fiel gls1 mentioned as wlell asdin article, said layer beingintegtrally merged, fused, many 0 er p aces. e previous y use pow er orjoined to the metallic ma erial net work permetallurgy processesemploying simple pressing meating the pores of the skeleton. The layerof 3nd gintering opteragions lwltlttl inixturdes 0ft p0 W- metal isformed of suificient thickness to suitably e e 1811 S ave 1ml 3 1011s 10 protect the article from corrosion. herent po os ty o the article a dfi e grain Size The skeleton is selected from materials so as and weakgrain boundar es of the resulting structo have high hot tensilestrength, high hot fatigue ture, all of which contribute to unfavorablehot strength, and high resistance to creep at elevated tensi e t e gthot t e Strength, d temperatures. The infiltrant metallic material isslstance o Creep at elevated tempfiraturesselected to have the desiredcorrosion resistance In pr v sly u p d r m l r y hand to impart thedesired physical properties to mques 1I1V1Vmg1mpTegPat1n a formed theskeleton. Preferably the layer of corrosion pact f sieletoni t g f gfresistant material is the same as that of the in- 01 1'8 IaC QTY 1113.ella. In 2. ere Olm 1S metallic material usually shaped by compressionin a mold and The article can be formed eflicaciously by perzfi isg jgfi ggg igg fg 2315 353 2; forming the impregnation step with theskeleton and sintered, a second or auxiliary lower melting g i figi igifii 223 533? i gi gi fi g metal is brought into Contact with theskeleton m kel t 1 t in a suitable ceramic or metallic vessel and heat eon m P fS a f or Que applied so as to Hquefy the second metal, andcondition. The infiltrant nietal wfll completely cause the Second orauxiliary metal to be drawn fi ll the moldso that the art cle will beaccurately into the Skeleton by capillary action In such a sized, andwill form a continuous layer over the process, the infiltrant metallicmaterial will not faces of article; skeleton can be completely cover theexterior face of the body. ranged in C ju W he mold so th t In theforming of the skeleton, diflicult probthere is sufficient clearance toform the desired lems arise when the shape is complex and irthickness ofthe coating layer. The thickness of regular, due to lack of uniformityin the pressed this layer of the infiltrant material is increased at thebase of the turbine blade for the shaped wheel engagingportions thereof.

The harder and more abrasive types of skeleton materials are diflicultto machine and this difliculty normally remains after the pores havebeen filled with the infiltrated material. It is desirable, therefore,to provide a layer of a skeletonfree infiltrant portion at places wherethe article is to be machined. This can be accomplished by placing theskeleton in a mold having an increased clearance between the mold wallsand the skeleton at areas where there is to be skeletoniree infiltrantmetal. The skeleton is impregnated while in said mold, preferably in apressure differential apparatus, so that the infiltrant completely fillsthe mold, thus leaving skeletonfree infiltrant metal of the desiredthickness in selected areas.

The refractory materials as employed in this invention have a lowcoefiicient of expansion, usually in the order of /3 to /2 of that ofsteel, or other metal alloys conventionally used in the constructionof'components of engines, turbines, and the like. This would result indifficulties if plain refractory compounds were used as structuralmaterials for such elements as turbine blades, buckets, valves and thelike.

In the present invention, the skeleton can be made of a refractorymaterial having the low coefficient of expansion and the desiredstrength characteristics at elevated temperatures. The infiltrantmaterial can be selected having a sufficiently high coefficient ofexpansion, so that the correct dimensional relationship can bemaintained with a supporting part for the composite article at allservice temperatures. The thickness of the infiltrant outside layer isincreased, as required, at the point of joinder of the blade with theelement to which it is to be attached, thus maintaining a fit withoutregard to temperature of operation.

The difierence in coefficients of expansion of the skeleton materialsand the infiltrant materials will result in other advantages, such asstrengthening of the composite structure, as will be explainedhereafter.

These and other features, advantages, and objects of the invention willbecome apparent from the following description and drawings.

In the drawings:

Fig. 1 shows a side view of one form of a turbine blade of the presentinvention.

Fig. 2 shows a front view of the blade of Fig. 1.

Fig. 3 shows an enlarged representation of a section of the compositebody at the point where the blade body joins the base thereof.

The invention will now be described in con junction with a turbineblade, such as is generally used in gas turbines.

The blade may have a tip or blade portion H] and a base portion H whichis machined to fit accurately into a suitably shaped notch or aperturein the turbine wheel.

It is desirable that the materials and dimensions of the base portionrelative to the turbine wheel be chosen so that the blade will remaintightly held under the elevated temperature conditions of operation.

In formation of the blade, the skeleton or high refractory phasedimensions or outline are diagrammatically indicated by the inner dashedlines l2 (Figs. 1, 2). The mold used during impregnation is arranged sothat the infiltrant metal or corrosion resistant phase will fill the themold and form the outside of the tip portion of the blade and will reachthe dashed lines l3 of the base ll. Thus there will be an excess of theinfiltrant metal at 14 which can be machined to the desired base shape[5. Such a formation of the composite article with a thickenedinfiltrant metal'portion may be termed undercasting. As previouslymentioned, the layer of infiltrant metallic material can be increased asdesired at other points such as where erosion takes place on the blade.

In Fig. 3, the skeleton or high refractory phase is indicated at IS, theparticles thereof being formed together with intercommunicating porestherebetween, said phase being continuous.

As an example, the skeleton material may be tungsten, molybdenum,titanium, tantalum, columbium, chromium, zirconium, or their alloys witheach other, or with iron, nickel, cobalt, or

their compounds of metalloidal character with carbon, boron, silicon,nitrogen, etc. Some examples of the aforementioned compounds ofmetalloidal character are tungsten carbide (WC), titanium carbide('IiC), molybdenum carbide (MOzC), tantalum carbide (TaC), columbiumcarbide (CbC), chromium carbide (ClsCz), zirconium carbide (ZrC),vanadium carbide (VC), tungsten boride (W132), titanium boride (TiBz),molybdenum boride (MOB), tantalum boride (TaB), columbium boride (CbB),chromium boride (CrB), zirconium boride (Z1'3B4), vanadium boride (VBz),thorium boride (ThBs); also stable refractory materials or compoundssuch as beryllium oxide, magnesium oxide, aluminum oxide, zirconiumoxide, silicon carbide, and boron carbide can be used, these beingstable at elevated temperatures.

' A typical composition of a homogeneous skeleton material as employedby this invention consists of by weight of tungsten carbide (WC), 25%titanium carbide (TiC) and 5% cobalt (C0),

the tungsten carbide (WC) and titanium carbide.v

(TiC) components being combined as a solid solution. Another typicalcomposition of a homogeneous skeleton material as employed by thisinvention consists of i5% by weight of tungsten carbide (WC), 25%titanium carbide (TiC), 25% chromium carbide (CrsCz) and 5% cobalt (Co),the tungsten carbide (WC) and titanium carbide (TiC) and chromiumcar-bide (CrsCz) components again being combined as a solid solution.

The infiltrant metallic material or corrosion resistant phase network isindicated at H! (Fig. 3), as entirely permeating all of theintercommunicating pores at the skeleton, thus forming a network asequally continuous as the skeleton. At 20 is seen the excess infiltrantmetal of sufiicient thickness to allow for machining and at 2! isindicated the layer of corrosion resistant metal on the exterior facesof the article integrally merged, fused or joined with the infiltrantmetal network permeating the pores of the skeleton. The representationin Fig. 3 corresponds to a single plane as is normally obtained in1netallo-- graphic procedures, the infiltrant metal being a continuousnetwork throughout the pores of the skeleton, this necessarily resultingfrom the manner in which the infiltrant metal fills the pores of theskeleton. Depending upon the alloyability between skeleton andinfiltrant materials, there may be formed an interphase along theboundaries of the same where they are in contact with each other. Thisinterphase may materially contribute to the strength of the compositestructure.

Again merely by way of example, the impregnating material may be iron,nickel, cobalt, chro mium and their alloys with each other, or theiralloys with the previously mentioned refractory metals, or metalcompounds as minor constituents. It is to be understood that theappropriate infiltrant having a dissimilar lower melting point relativeto the skeleton can be used, and that the word metal in the claim is tobe construed to include the aforementioned. A typical composition ofimpregnating material employed successfully by this invention comprisesan alloy containing 69% by Weight of cobalt, 25% chromium and 6%molybdenum. Another example is a material containing 50% by weight ofcobalt, 29% chromium, 15% nickel and 6% molybdenum. Still anotherexample is one containing 52% by weight of cobalt, 28% chromium, 11%nickel, and 9% tungsten. Another example contains 60% by Weight ofnickel, 16% molybdenum, 14% chromium, tungsten and 5% iron, while stillanother contains 60% by weight of chromium, 25% molybdenum and 15% iron.

As mentioned previously, the coeiiicient of expansion of the infiltrantphase is usually much higher than that of the skeleton phase.Consequently, because the infiltrant phase is carried out at a muchhigher temperature than the operating temperature of the article, therewill be a shrinkage of the infiltrant phase relative to the refractoryphase. The relationship of the coefiicients will be such as to createinternal stress conditions in the article, so that better elevatedtemperature strength and creep resistance will be obtained.

It is apparent that details of construction can be varied withoutdeparting from the spirit of the invention except as defined in theappended claims.

We claim:

1. A composite material shaped turbine blade having a base portionengageable with a turbine wheel for use at elevated temperatures incorrosive atmospheres, said blade being composed of substances ofdifferent melting points and having a sintered porous skeleton of highermelting point normally corrodible at the temperatures of operation andformed with intercommunicating pores substantially throughout itsentirety, the pores thereof being permeated with an infiltrant metalhaving corrosion resistant properties under the conditions of operationand a substantially continuous controlled layer of said infiltrant metalof predetermined thickness on the exterior faces of said blade toprotect the same, said layer being integrally fused with the metalpermeating said pores, the layer being thickened at the base portion ofthe blade for the shaped wheel engaging portions thereof.

2. In a composite material shaped turbine blade according to claim .1,the sintered porous skeleton consisting of titanium carbide.

3. In a composite material shaped turbine blade accoridng to claim 1,the sintered porous skeleton consisting of tungsten carbide.

4. In a composite material shaped turbine blade according to claim 1,the sintered porous skeleton consisting of 70 weight per cent tungstencarbide, 25 weight per cent titanium carbide and 5 Weight per centcobalt.

5. In a composite material according to claim 1, ton consisting of bide,25 weight Weight per cent per cent cobalt.

shaped turbine blade the sintered porous skeleweight per cent tungstencarper cent titanium carbide, 25 chromium carbide and 5 weight CLAUS G.GOETZEL. JOHN L. ELLIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,192,792 Kurtz Mar. 5, 19402,198,240 Boegehold Apr. 23, 1940 2,239,800 Vogt et al Apr. 29, 19412,381,459 Merrick Aug. 7, 1945 2,422,439 Schwarzkopf June 17, 19472,456,779 Goetzel Dec. 21, 1948

1. COMPOSITE MATERIAL SHAPED TURBINE BLADE HAVING A BASE PORTIONENGAGEABLE WITH A TURBINE WHEEL FOR USE AT ELEVATED TEMPERATURES INCORROSIVE ATMOSPHERES, SAID BLADE BEING COMPOSED OF SUBSTANCES OFDIFFERENT MELTING POINTS AND HAVING A SINTERED POROUS SKELETON OF HIGHERMELTING POINT NORMALLY CORRODIBLE AT THE TEMPERATURES OF OPERATION ANDFORMED WITH INTERCOMMUNICATING PORES SUBSTANTIALLY THROUGHOUT ITSENTIRETY, THE PORES THEREOF BEING PERMEATED WITH AN INFILTRANT METALHAVING CORROSION RESISTANT PROPERTIES UNDER THE CONDITIONS OF OPERATIONAND A SUBSTANTIALLY CONTINUOUS CONTROLLED LAYER OF SAID INFILTRANT METALOF PREDETERMINED THICKNESS ON THE EXTERIOR FACES OF SAID BLADE TOPROTECT THE SAME, SAID LAYER BEING INTEGRALLY FUSED WITH THE METALPERMEATING SAID PORES, THE LAYER BEING THICKENED AT THE BASE PORTION OFTHE BLADE FOR THE SHAPED WHEEL ENGAGING PORTIONS THEREOF.